Chinese activist Xu Zhiyong, in police custody since mid-July, has released a video message from his cell, calling on his compatriates "to be citizens" and hold up the rights and obligations laid down by the nation's constitution.

"No matter how corrupted and absurd society is, this country needs some courageous citizens to stand up, stick to their faith and realise rights, obligations and dreams," said Xu, a prominent leader of the New Citizen Movement.

The video message appeared to have been recorded in secret on a phone on August 1 by someone visiting him in detention. Xu is seen wearing a orange jail vest and speaking from behind bars.

The 40-year-old law lecturer at Beijing University of Posts and Telecommunications is one of the founders of the New Citizen Movement, which has called on Chinese officials to reveal their assets and respect citizen's constitutional rights.

Rights laid down in the Chinese constitution, such as the freedom of speech, press and assembly, are not enforced by Chinese courts.

Xu was arrested on July 16 on charges of "disturbing public order", after spending more than three months under house arrest at his Beijing home.

He is one of least 16 people involved in the citizen campaign who been arrested in China over the last months as the movement had gathered pace. Searches for Xu's name and "constitutional rule" are blocked on Chinese microblogs.

Xu said in the video message, in an apparently sarcastic tone, that he had committed three "crimes": to call for the realisation of citizens' constitutional rights and obligations, for equal opportunity in education and for the declaration of assets by officials.

The People's Daily attacked the citizen movement's in a series of front-page commentaries in its overseas edition this week. In one commentary on Wednesday, the Communist Party's leading paper said that the activists' call for constitutional governance was "wishful thinking".

President Xi Jinping had raised hopes in December when he declared that China had to "firmly establish, throughout society, the authority of the constitution". At a Politburo meeting in February, he said "no organisation or individual should be put above the constitution".